Chair back



FIG. 1 is a perspective view of the present invention;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a right-side elevational view thereof (the left-side elevational view being a mirror image);

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

The broken lines shown are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a chair back, as shown and described. 